1. Field of the Invention
The invention relates to improved methods for producing methylene malonate monomers and to the use or application of methylene malonate monomers prepared by the methods of the invention as commercial products and compositions, including, for example, monomer-based products (e.g., inks, adhesives, coatings, sealants or reactive molding) and polymer-based products (e.g., fibers, films, sheets, medical polymers, composite polymers and surfactants).
2. Background
Methylene malonates are compounds having the general formula (I):
wherein R and R′ may be the same or different and may represent nearly any substituent or side-chain. Such compounds have been known since 1886 where the formation of diethyl methylene malonate was first demonstrated by W. H. Perkin, Jr. (Perkin, Ber. 19, 1053 (1886)).
These compounds have the potential to form the basis of a highly valuable novel large-scale platform for the chemical synthesis of a new order of raw materials for the generation of a wide variety of new chemical products, including inks, adhesives, coatings, sealants, molding, fibers, films, sheets, medical polymers, composites, surfactants and the like. While the potential is there for such materials, methylene malonates or materials made therefrom have found very limited commercial success owing to the difficulty of their production, including poor and erratic yields, lack of reactivity, and general instability of the monomer products. These difficulties stem from the deficiencies in the methods developed over the years which have proposed various schemes for synthesizing methylene malonates.
However, while such earlier methods for producing methylene malonates have been known for many years, these prior methods suffer significant deficiencies which preclude their use in obtaining commercially viable monomers. Such deficiencies include unwanted polymerization of the monomers during synthesis (e.g., formation of polymers or oligomers or alternative complexes), formation of undesirable side products (e.g., ketals or other latent acid-forming species which impede rapid polymerization), degradation of the product, insufficient and/or low yields, and ineffective and/or poorly functioning monomer product (e.g., poor adhesive characteristics, stability, or other functional characteristics), among other problems. The overall poorer yield, quality, and chemical performance of the monomer products formed by prior methods has impinged on their practical use in the production of the above commercial and industrial products. No viable solutions to solve the aforementioned problems have yet been proposed, accepted and/or recognized and certainly do not exist currently in the industry.
For example, in U.S. Pat. No. 2,330,033 to Gaetano D'Alelio (“the '033 patent”), methylene malonic esters are prepared by condensing a malonic ester with formaldehyde under alkaline conditions, acidifying with acetic acid and dehydrating the mass and distilling the methylene malonic ester. In each example of the '033 patent, the condensation reaction is acidified using acetic acid. Furthermore, the ester is described as polymerizing spontaneously in the absence of inhibitors. Thus, the reaction conditions described in the '033 patent would have led to the undesirable premature polymerization of the monomer and the production of deleterious side products. Further, the reference does not even recognize the formation of such deleterious side products, let alone does it provide any teachings or suggestions as to how to avoid or eliminate the formation of these impurities. Accordingly, the methylene malonates purportedly formed by this process are impractical for use in the production of viable commercial and industrial products.
Similarly, in U.S. Pat. No. 2,313,501 to Bachman et al. (“the '501 patent”), methylene dialkyl malonates are prepared by the reaction of dialkyl malonates with formaldehyde in the presence of an alkali metal salt of a carboxylic acid in a substantially anhydrous carboxylic acid solvent. The method of the '501 patent purports to provide higher yields than the prior methods of condensing formaldehyde with a dialkyl malonate in the presence of a base. In the '501 patent, methylene diethyl malonate is distilled directly from the reaction mixture under sub-atmospheric pressure. The ester is described as forming a soft waxy white polymer upon standing, indicating the presence of a high degree of deleterious side products. The '501 patent does not even recognize the formation of such deleterious side products, let alone does it provide any teachings or suggestions as to how to avoid or eliminate the formation of such impurities. Thus, the methylene malonates purportedly formed by this process are highly unstable and are impractical for use in the production of viable commercial and industrial products.
Furthermore, in U.S. Pat. No. 3,197,318 to Halpern et al. (“the '318 patent”), dialkyl methylene malonic acid esters are prepared by condensing dimethylmalonate with formaldehyde in the presence of acetic acid and an acetate of a heavy metal at 100-110° C. The reaction mixture is directly distilled under reduced pressure. The '318 patent states that in the anhydrous composition, the reaction either fails to occur or is greatly delayed by the inhibitor up to the time when the effectiveness of the inhibitor is reduced by contact of moisture therewith (from occluded surface water on glass, metal or the like). The unfavorable reaction conditions described in this reference would have led to the production of deleterious side products. The '318 patent does not even recognize the formation or presence of these impurities, let alone offer teachings or suggestions as to how to avoid or eliminate their formation. Accordingly, the methylene malonates purportedly formed by the process of the '318 patent would have been impractical for their use in the production of viable commercial products.
Also, in U.S. Pat. No. 3,221,745 to Coover et al. (“the '745 patent”), monomeric dialkyl esters of methylene malonic acid are purportedly prepared in high purity because even with small amounts of impurities that influence polymerization the adhesive utility will be impaired. The '745 patent describes removing all impurities to levels below 100 parts-per-million preferably below 10 parts-per-million. The monomers are prepared by hydrogenating the olefinic bond of a dialkyl alkoxy-methylenemalonate in the presence of a hydrogenation catalyst and pyrolyzing the reaction product. The '745 patent states that these high purity materials polymerize and form firm bonds in situ rapidly, within seconds. Indeed, the '745 patent, like related U.S. Pat. No. 3,523,097 to Coover et al. (“the '097 patent”), requires the use of an acidic stabilizer to enhance shelf-life and to prevent premature polymerization. However, the high temperature conditions of the pyrolysis reaction invariably results in the formation of unwanted and deleterious side products and is a much more expensive and difficult synthesis process for preparing methylene malonate as compared to the Knovenagel reaction with formaldehyde. Thus, the monomer purportedly formed by the processes of the '745 and '097 patents is impractical for use in the production of viable commercial and industrial products.
Still further, in U.S. Pat. No. 3,758,550 to Eck et al. (“the 550 patent”) report on a general process for producing methylene malonic esters of the general formula CH2═C(—CO2R)2, by reacting paraformaldehyde in glacial acetic acid in the presence of a catalyst to form a product in the form of a “gel” which is then “cracked” at high temperature distillation. The reaction is conducted over long periods of time, including up to 15 hours, and produces a substantial amount of deleterious side products, as evidenced by the gelatinous characteristics of the product. Further, the '550 patent contains no support showing the functionality of the monomers produced. Due to the likely presence of high levels of impurities, the functionality of the monomers produced by the '550 patent would likely be substantially compromised.
Citing numerous disadvantages of the foregoing processes, which disadvantages were said to make them difficult, if not impossible, to provide commercially viable monomers, Bru-Magniez et. al. (U.S. Pat. No. 4,932,584 and U.S. Pat. No. 5,142,098) (“the '584 and '098 patents”) developed a process whereby anthracene adducts were prepared by reacting mono- or di-malonic acid ester with formaldehyde in the presence of anthracene, most preferably in a non-aqueous solvent medium in the presence of select catalysts. According to these patents, the anthracene adducts were said to be readily produced in high yields with the desired methylene malonates obtained by stripping them from the anthracene adduct by any of the known methods including heat treatment, thermolysis, pyrolysis or hydrolysis; preferably heat treatment in the presence of maleic anhydride. The resultant crude products were then subjected to multiple distillations, preferably lower temperature distillations under vacuum, to recover the purified methylene malonates. Despite the claim to high yields, their crude yields were generally in the range of 21-71%, and more importantly, nothing is taught with respect to the purity of the material obtained.
While the use of intermediate adducts promoted higher yields and allowed greater versatility, particularly with respect to the broader variety of methylene malonates capable of being produced, lingering problems persisted, namely batch-to-batch inconsistency and the general instability of the process as well as the so-formed crude and final products, especially in bulk storage, and of formulated products, such as adhesives, made with the same. Additionally, the adduct routes involve considerable added expense, particularly in light of the need for the additional reactants and other materials, added production steps and time, new energy requirements and environmental concerns, and the like. Furthermore, despite their advances, these processes have yet to fully or even adequately address, particularly from a commercial viability standpoint, the underlying and critical problems evidenced by the continuing inconsistency in the production of the methylidene malonates, particularly as reflected by the ongoing instability of the reaction mix particularly during the distillation and recovery of the desired product as well as of the recovered product. It is this erratic nature of the production process and resultant product and the attendant costs associated therewith that compromises and overshadows the commercial value and opportunity for these products.
Similar conclusions may be drawn from other representative prior references that purport to teach the synthesis of methylene malonates, including, for example, U.S. Pat. Nos. 3,557,185; 3,975,422; 4,049,698; 4,056,543; 4,160,864; and 6,106,807. None of these references, however, recognize the same problems discussed above, including the formation of deleterious side products, such as, ketals and other latent acid-forming species which impede monomer performance, the occurrence of unwanted polymerization (e.g., unintended formation of polymers, oligomers or alternative complexes) and the general degradation and instability of the monomer products which together substantially impedes the production of high-quality methylene malonate monomers having commercial viability.
In view of the above art, there remains no known single viable commercially suitable method or process for the chemical synthesis of methylene malonate monomers which may be utilized to produce these important raw materials for the generation of a wide variety of commercial and industrial products. Thus, a need exists for improved methods for synthesizing methylene malonate monomers that are capable of being viably used in commercial and industrial applications.
The present invention solves the aforementioned problems in the synthesis of methylene malonate monomers and paves the way to a commercially viable source of an important raw material.